Investigators at the Harvard School of Public Health analyzed data from a study of twins who served during the Vietnam War conclude that those who smoked had twice the risk of acquiring PTSD.. Investigators at the Harvard School of Public Health analyzed data on 6744 Vietnam veterans in the twin registry (a national registry of all male-male twin pairs who served in the military during the Vietnam era and who were interviewed in 1991-2) to explore the association between nicotine dependence and the risk of acquiring posttraumatic stress. About half the twins were identical.

The study concluded that those who smoke have twice the risk of suffering from posttraumatic stress disorder (PTSD), and that smoking is a major risk factor for developing PTSD.

This finding supports the hypothesis that nicotine stimulates some of the same neurobiological pathways - the dopaminergic pathway associated with reward and fear - involved in stress and addiction, and that smoking may sensitize these pathways, so a subsequent severe stressor is more likely to induce PTSD. It was not clear whether quitting smoking would reduce the risk of PTSD.

Citation: Koenen KC, Hitsman B, Lyons MJ, Niaura R, McCaffery J, Goldberg J, Eisen SA, True W, Tsuang M.A Twin Registry Study of the Relationship Between Posttraumatic Stress Disorder and Nicotine Dependence in Men. Arch Gen Psychiatry. 2005 Nov; 62 (11): pages 1258-1265.